Receiving circuit and electronic apparatus for optical communication

ABSTRACT

In an optical communication-use receiving circuit of the present invention, the pulse width of the received pulse which is a binary signal corresponding to the signal optical pulse is specified by using an integration circuit and a trigger generating circuit. If the pulse width of the received pulse is not shorter than a predetermined value, a signal having a fixed pulse width is outputted as an output signal from a one-shot pulse generating circuit, so that a pulse having a constant pulse width corresponding to the specified communication speed is outputted. Accordingly, if the pulse width deriving from the signal optical pulse is larger than a certain value, the communication is deemed as a low-speed communication, and a pulse having a constant pulse width corresponding to the communication speed is outputted. As a result, it is possible to realize a small-size receiving circuit and a small-size electronic device which require no external switching-over terminal.

This Nonprovisional application claims priority under 35 U.S.C. § 119(a)on Patent Application No. 2004/203959 filed in Japan on Jul. 9, 2004,the entire contents of which hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to a receiving circuit an electronicapparatus for use in an optical communication using light such as aninfrared ray.

BACKGROUND OF THE INVENTION

A size of a transmitting/receiving module for use in infrared datacommunication has been reduced. Further, performance of such atransmitting/receiving module has been improved, and its processingspeed has been accelerated. In regard to the acceleration of theprocessing speed, it is necessary that the transmitting/receiving modulebe capable of handling a conventional low-speed communication as well asa high-speed communication, so that the transmitting/receiving module iscompatible, in terms of communication, with a conventional low-speeddevices. In short, it is necessary that the transmitting/receivingmodule support the low-speed communications as well as the high-speedcommunications. The most important problem to be solved for achievingthis is performance of a receiving device. In the receiving device, apulse needs to be reproduced based on a communication speed, and thispulse is transmitted to a controller LSI in a latter stage. Thisreceiving device needs to support various communication speeds.

An example of the prior art is disclosed in Japanese Unexamined PatentApplication No. 2000-115078 (Tokukai 2000-115078; published on Apr. 21,2000).

FIG. 9 is a block diagram illustrating a conventional receiving systemfor use in a infrared data communication. In a typical arrangement of areceiving circuit 101 for use in an optical communication, aphotocurrent signal (optical signal pulse) is inputted via a photodiodechip (PD), and is amplified in amplifying circuits 21 and 22 in anintegrated receiving chip. Then, in a hysteresis comparator 23, apulse-reshaping process is carried out with respect to the amplifiedphotocurrent signal by comparing the amplified photocurrent signal witha threshold “Thresh” for use in measuring a signal, so as to convert theamplified photocurrent signal into a digital signal (received pulse).Then, the digital signal is outputted in the form of pulse to a receivedoutput (VO). The received output (VO) is connected to the controller LSI(not shown), and the digital signal outputted from the received outputis processed in the control LSI. In order to accelerate thecommunication speed, frequency bands of the amplifying circuits 21 and22 are increased so as to correspond to the high speed communication.Alternatively, performance of the pulse generating circuit (hysteresiscomparator circuit 23) is improved. However, for example, the followingproblems occur when increasing the frequency bands or accelerating theperformance of the pulse generating circuit. Namely, an internal noiselevel is increased in the receiving device on account of an increase inthe frequency bands. Further, an increase of unwanted noise or the likeproblem takes place on account of an acceleration in the processingspeed of the pulse generating circuit.

In view of the foregoing problems of noise, a common infrared datacommunication standard known as IrDA defines standards of receptionsensitivity which are different from one another on a transmission speedbasis. In a low-speed communication of 2.4 kbps to 115.2 kbps, thesensitivity of the receiving device is defined as 4 μW/cm². In ahigh-speed communication of over 115.2 kbps (e.g. 576 kbps, 1.152 Mbps,4 Mbps, and 16 Mbps), the sensitivity is defined as 10 μW/cm². That is,the sensitivity is so defined that the sensitivity in the high-speedcommunication is 2.5 times of the sensitivity in the low-speedcommunication.

Conventionally, the receiving device has been so arranged thatproperties of the receiving circuit are switched over depending on thecommunication speeds. In the case of FIG. 9, a terminal (MODE) is theterminal for switching the properties.

However, due to the trend of reducing a size of an apparatus having aninfrared transmitting/receiving module device, a size of the deviceneeds to be even smaller, and the number of terminals in the deviceneeds to be reduced. This calls for a measure which eliminates a need ofswitching-over terminals.

SUMMARY OF THE INVENTION

In view of the foregoing problems, the present invention is made, and itis an object of the present invention to provide a receiving circuit andan electronic apparatus for use in an infrared data communication, whoserespective sizes can be reduced, the receiving circuit and theelectronic apparatus which need no external switching over terminal.

In order to achieve the foregoing object, a receiving circuit of thepresent invention is a receiving circuit, for use in an opticalcommunication, from which an output signal is outputted in accordancewith a signal optical pulse incident to a light-receiving element, thereceiving circuit including: a variable output circuit for (I) detectinga pulse width of the signal optical pulse, (II) determining a pulsewidth of the output signal in accordance with the pulse width of thesignal optical pulse, and (III) outputting the output signal.

In the configuration, the pulse width of the signal optical pulse ismeasured, and the output signal whose pulse width is determined inaccordance with the pulse width of the signal optical pulse isoutputted. This allows outputting of an output signal based on thesignal optical pulse in the receiving circuit. Further, it is notnecessary to separately provide an external terminal for instructingswitching over. Therefore, a space for the external terminal is nolonger necessary. As a result, it is possible to realize a receivingcircuit whose size is reduced, and which requires no external switchingover terminal.

Further, in addition to the foregoing configuration, the receivingcircuit of the present invention may be so adapted that: the variableoutput circuit includes a first pulse generating circuit generating areceived pulse by comparing an electric signal converted from the signaloptical pulse with a threshold, the received pulse being a digitalsignal; and either the received pulse generated by the first pulsegenerating circuit or a pulse having a different pulse width from thatof the received pulse is selectively outputted as an output signal, inaccordance with the pulse width of the signal optical pulse.

In the foregoing configuration, when the output signal is outputted, thepulse width of the output signal is switched over in accordance with thepulse width of the inputted signal optical pulse. This allows theswitching over of an output signal based on the signal optical pulse inthe receiving circuit. Further, it is not necessary to separatelyprovide an external terminal for instructing switching over. Therefore,a space for the external terminal is no longer necessary. As a result,in addition to the foregoing effects, the realization of the receivingcircuit is significantly simplified.

Further, in addition to the foregoing configuration, the receivingcircuit of the present invention is so adapted that: the variable outputcircuit includes a second pulse generating circuit for generating asignal having a predetermined pulse width corresponding to a low-speedcommunication; and if it is judged that a pulse width of an output fromthe first pulse generating circuit exceeds a predetermined value, asignal generated by the second pulse generating circuit is outputted asthe output signal, instead of outputting the received pulse.

In the foregoing configuration, the pulse width of the received pulse(i.e., a binary signal) corresponding to the signal optical pulse isspecified. If the pulse width of the received pulse exceeds apredetermined value, a signal having a fixed pulse width is outputted asthe output signal. Accordingly, if the pulse width deriving from thesignal optical pulse is larger than a certain value, the communicationis deemed as to be a low-speed communication, and a pulse having aconstant pulse width corresponding to the communication speed isoutputted. As a result, in addition to the foregoing effects, it ispossible to switch over the communication speed to an appropriate speedfor the low-speed communication, in accordance with the signal opticalpulse in the receiving circuit.

Further, in addition to the foregoing configuration, the receivingcircuit of the present invention is so adapted that: the variable outputcircuit includes (I) a trigger generating circuit for generating atrigger signal when a pulse generating time of the first pulsegenerating circuit exceeds a first predetermined period, and (II) atimer circuit for generating a pulse having a second predetermined pulsewidth, in response to the trigger signal from the trigger generatingcircuit; if the timer circuit outputs no pulse, a pulse outputted fromthe first pulse generating circuit is outputted as the output signal;and if the timer circuit outputs a pulse, a pulse outputted from thesecond pulse generating circuit is outputted as the output signal.

In the foregoing configuration, the first pulse generating circuitoutputs an ultimate output signal, while the timer circuit is notoutputting the output pulse. On the contrary, the second pulsegenerating circuit outputs the ultimate output pulse, while the timercircuit is outputting the output pulse. In other words, while the timercircuit is not outputting the output pulse, it is acknowledged that thecommunication speed is high, and output pulse having the pulse width forthe high-speed communication is outputted. On the contrary, while thetimer circuit is outputting the output pulse, it is acknowledged thatthe communication speed is low, and an output pulse having the pulsewidth for the low-speed communication is outputted. Accordingly, inaddition to the foregoing effects, the foregoing configuration allowssimple switching over of the communication speed according to the signaloptical pulse.

Further, in addition to the foregoing configuration, the receivingcircuit of the present invention is so adapted that the first pulsegenerating circuit includes a one-shot pulse generating circuit formaintaining the pulse width being outputted at a constant value, theone-shot pulse generating circuit to which the received pulse isinputted.

With the foregoing configuration, in the first pulse generating circuit,the pulse width of the output from the one-shot pulse generating circuitis kept constant. Accordingly, in addition to the foregoing effects, itbecomes possible to prevent generation of a wrong pulse and distortionin the pulse width of the received output, during the high-speedcommunication.

Further, in addition to the foregoing configuration, the receivingcircuit of the present invention is so adapted that the first pulsegenerating circuit includes a delay circuit to which the received pulseis inputted.

In the foregoing configuration, the output of the first pulse generatingcircuit delays by one pulse or the like. Accordingly, in addition to theforegoing effects, it is possible to prevent a width of a leading pulseof a set of signals from being stretched, at the time of acknowledgingthat the communication speed is low.

Further, in addition to the foregoing configuration, the receivingcircuit of the present invention further includes a delay circuitconnected to an output of the one-shot pulse generating circuit.

In the foregoing configuration, the output of the first pulse generatingcircuit delays by one pulse or the like. Accordingly, in addition to theforegoing effects, it is possible to prevent a leading pulse of a set ofsignals from being stretched, at the time of acknowledging that thecommunication speed is low.

Further, in addition to the foregoing configuration, the receivingcircuit of the present invention is so adapted that a length of thefirst predetermined period is set between a pulse width of the outputpulse from the second pulse generating circuit and a pulse width of theoutput pulse from the first pulse generating circuit.

In the foregoing configuration, the length of the first predeterminedperiod is set between the pulse width of the output pulse from thesecond pulse generating circuit and the pulse width of the output pulsefrom the first pulse generating circuit. Therefore, the value of thefirst predetermined period (T1) is set between values of respectivepulse widths of two communication speeds to be distinguished from eachother. Accordingly, in addition to the foregoing effects, it alsobecomes possible to optimize the process of specifying the communicationspeed, in a case of adopting the common infrared data communicationstandard IrDA.

Further, in addition to the foregoing configuration, the receivingcircuit of the present invention is so adapted that the firstpredetermined period is between 521 n sec. and 1.41 μsec.

In the foregoing configuration, the first predetermined period isbetween 521 n sec. and 1.41 μsec. Accordingly, in addition to theforegoing effects, it also becomes possible to distinguish thecommunication speed into (I) a communication speed of 576 kbps orhigher, and (II) a communication speed of 115.2 kbps or lower. Thisallows outputting of an optimum received output pulse suitable for thecommunication speed.

Further, in addition to the foregoing configuration, the receivingcircuit of the present invention is so adapted that the secondpredetermined period is equal to or longer than a maximum intervalbetween a pulse and another pulse.

In the foregoing configuration, the second predetermined period is equalto or longer than the maximum interval of a pulse and another pulse.Accordingly, in addition to the foregoing effects, it also becomespossible to maintain a status for the specified communication speedwithout fail until the end of the communication without additionalterminal or control for resetting the second predetermined period isnecessary.

Further, in addition to the foregoing configuration, the receivingcircuit of the present invention is so adapted that the secondpredetermined period is 1.04 m sec. or longer.

In the foregoing configuration, the second predetermined period is 1.04m sec. or longer. Accordingly, in addition to the foregoing effects, italso becomes possible to maintain the status without fail by setting thetimer, so that the second predetermined period is equal to or longerthan the maximum interval of a pulse and another pulse.

Further, in addition to the foregoing configuration, the receivingcircuit of the present invention further includes: an amplifying circuitfor amplifying an electronic signal converted from the signal opticalpulse, the variable output circuit switching over, in accordance with acommunication speed, a frequency band of the amplifying circuit duringthe period when the pulse of the second predetermined period exists.

In the foregoing configuration, the variable output circuit switchesover, in accordance with a communication speed, the frequency band ofthe amplifying circuit during the period when the pulse of the secondpredetermined period exists. Accordingly, in addition to the foregoingeffects, it also becomes possible to optimize the receiving circuitaccording to the communication speed. Further, it is possible torealizes an optimum S/N ratio according to the specified communicationspeed.

Further, in addition to the foregoing configuration, the receivingcircuit of the present invention is so adapted that, during the periodwhen the pulse of the second predetermined period exists, the variableoutput circuit switches over a response speed of the variable outputcircuit, in accordance with a communication speed.

With the foregoing configuration, the variable output circuit switchesover the response speed thereof in accordance with the communicationspeed, during the period when the pulse of the second predeterminedperiod exists.

Accordingly, in addition to the foregoing effects, it also becomespossible to optimize the receiving circuit according to thecommunication speed. Further, it is possible to realizes an optimum S/Nratio according to the specified communication speed.

Further, an electronic device of the present invention having areceiving circuit is so adapted that the receiving circuit is any one ofthe foregoing receiving circuits.

In the foregoing configuration, one pulse width is selected from aplurality of pulse widths, in accordance with the pulse width of thesignal optical pulse. Then, the output signal having the selected pulsewidth is outputted as the output signal. This allows outputting of anoutput signal based on the signal optical pulse in the receivingcircuit. Further, it is not necessary to separately provide an externalterminal for instructing switching over. Therefore, a space for theexternal terminal is no longer necessary. As a result, it is possible to(I) realize a receiving circuit whose size is reduced, and whichrequires no external switching over terminal, and (II) realize anelectronic device whose size can be reduced.

Additional objects, features, and strengths of the present inventionwill be made clear by the description below. Further, the advantages ofthe present invention will be evident from the following explanation inreference to the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating a configuration of a receivingcircuit of the present invention for use in an infrared datacommunication.

FIG. 2 is a block diagram illustrating another configuration of thereceiving circuit of the present invention for use in an infrared datacommunication.

FIG. 3 is a block diagram illustrating still another configuration ofthe receiving circuit of the present invention for use in an infrareddata communication.

FIG. 4 is a block diagram illustrating yet another configuration of thereceiving circuit of the present invention for use in an infrared datacommunication.

FIG. 5 is a diagram illustrating exemplary waveforms of nodes in anequivalent circuit block of the present invention in a high-speed mode.

FIG. 6 is a diagram illustrating exemplary waveforms of nodes in theequivalent circuit block of the present invention in a low-speed mode.

FIG. 7 is a diagram illustrating exemplary waveforms of nodes in theequivalent circuit block of the present invention in a low-speed mode,in a case where a received pulse is delayed.

FIG. 8 is a diagram illustrating communication speeds and pulse widthsdefined under an infrared data communication standard.

FIG. 9 is a block diagram illustrating an exemplary configuration of aconventional receiving circuit for use in an infrared datacommunication.

FIG. 10 is a diagram illustrating exemplary waveforms in theconventional receiving circuit for use in an infrared datacommunication.

FIG. 11 is a diagram illustrating an example of noise generation causedby an interference of input and output signal waveforms in the receivingcircuit for use in the infrared data communication.

DESCRIPTION OF THE EMBODIMENTS

The present embodiment deals with an example of applying the presentinvention to a common infrared data communication standard called IrDA.However, the present invention is not limited to such an example.Further, light being used is not limited to an infrared ray. Note thatthe same symbols are given to the members that have the same functionsas those illustrated in FIG. 9, and the descriptions of those membersare omitted here.

FIG. 1 is a block diagram of an infrared-ray-receiving equivalentcircuit. A configuration of an entire receiving circuit 11 for use in anoptical communication includes: (I) the comparator 23 described in“BACKGROUND ART” with reference to FIG. 9; and (II) a switching circuit12 provided at an output end of the comparator 23, the switching circuit12 as an automatic communication speed switching circuit block forautomatically switching over a communication speed. Thus, a variableoutput circuit includes the amplifying circuits 21 and 22, thehysteresis comparator circuit 23, and the switching circuit 12.

The switching circuit 12 includes: (I) an integration circuit 31 formeasuring a pulse width of a comparator output (c); (II) aone-shot-timer-input-use trigger generating circuit 32 for generating atrigger pulse when the pulse width of the comparator output (c) islonger than a first predetermined period T1, the trigger generatingcircuit 32 being connected to the integration circuit 31; (III) aone-shot pulse generating circuit 33 serving as a timer circuit, theone-shot pulse generating circuit 33 for generating a pulse of a secondpredetermined period T2; and (IV) a one-shot pulse generating circuit 34(second pulse generating circuit) for generating a pulse of a thirdpredetermined period T3. The one-shot timer generating circuit 33 andthe one-shot timer generating circuit 34 are respectively connected tothe trigger generating circuit 32. Further, a logic circuit having thefollowing logic is connected to outputs of the one-shot timer generatingcircuit 33, the one-shot timer generating circuit 34, and the hysteresiscomparator 23. A pulse is outputted, via the logic circuit, to areceived output (VO) serving as an output of the receiving circuit.

The logic of the logic circuit is as follows. Namely, while the one-shotpulse generating circuit 33 is generating the pulse of the secondpredetermined period, the one-shot pulse generating circuit 34 outputsthe pulse of the third predetermined period to the received output (VO).On the contrary, while the one-shot pulse generating circuit 33 is notgenerating the pulse of the second predetermined period, the output fromthe comparator output (c) is outputted, as it is, to the receivedoutput. Thus, in accordance with the pulse width of the signal opticalpulse, the output signal outputted from the received output is switchedover between a received pulse (digital pulse from the hysteresiscomparator 23) and a pulse having a different pulse width from that ofthe received pulse.

More specifically, when the trigger pulse is generated at the node (e),it is acknowledged that the pulse width of the received pulse generatedby the hysteresis comparator circuit 23 is longer than the predeterminedwidth (T1), and that the pulse width of the signal optical pulse istherefore longer than the predetermined width (T1). As a result, it isjudged that the communication is in a low-speed mode. In this case, theone-shot pulse generating circuit 33 generates the pulse of the secondpredetermined period. Then, based on the foregoing logic, the one-shotpulse generating circuit 34 whose output pulse has the pulse width ofthe third predetermined period outputs, to the received output VO, apulse having a pulse width for the low-speed communication. Asdescribed, it is judged whether or not the pulse width of the receivedpulse being outputted from the hysteresis comparator circuit 23 servingas a first pulse generating circuit is longer than the predeterminedvalue (T1). If the pulse width is longer than the predetermined value(T1), a signal having a constant pulse width for the low-speedcommunication is outputted as the output signal from the one-shot pulsegenerating circuit 34 serving as a second pulse generating circuit,instead of outputting the reception signal as the output signal.

Once it is judged that the communication is the low-speed communication,the low-speed communication is maintained for a period corresponding tothe second predetermined pulse width of the one-shot pulse generatingcircuit 33, and transmission of the received pulse from the comparatoroutput to the received output (VO) is blocked during this period.

FIG. 6 is a timing chart showing exemplary waveforms of respective nodesin the circuit block, during the low-speed mode. The first, second, andthird predetermined periods (pulse widths) are respectively indicated byT1, T2, and T3 in FIG. 6. Note that the pulse width (T3) of a node (g);i.e., the pulse width of the output pulse from the one-shot pulsegenerating circuit 34, is longer than the pulse width of a node (c);i.e., the pulse width of the output pulse from the hysteresis comparatorcircuit 23. Further, the pulse width of the node (c), and the pulsewidth (T3) of the node (g) are respectively 434 n sec, 1.63 μsec., orthe like as shown in FIG. 8.

In this example, the predetermined pulse width (T3) is outputted to thereceived output (VO) during the low-speed communication. This is acommon technology for restraining a malfunction due to distortion in anamplified waveform caused by (I) internal noise of the receiving circuitand/or (II) an interference of a received input and the received output.A value of the T3 can be selected in accordance with the speed of thelow-speed communication.

Next, if the trigger pulse is not generated at the node (e), it isacknowledged that the pulse width of the received input pulse is equalto or less than the predetermined pulse width (T1). Thus, it is judgedthat the communication is in the high-speed mode. In this case, thelogic is such that the pulse width of the pulse from the comparatoroutput is outputted, as it is, to the received output (VO).

FIG. 5 is a timing chart showing exemplary waveforms of the nodes in thecircuit block, during the high-speed mode.

As described, in the present embodiment, the pulse width of the signaloptical pulse is measured. Then, in accordance with the measured pulsewidth, the pulse width of the output signal is determined, and theoutput signal having the pulse width thus determined is outputted. Forexample, in accordance with the pulse width of the signal optical pulse,one pulse width is selected from a plurality of pulse widths includingthe pulse width corresponding to the pulse width of the signal opticalpulse. Then, the output signal having the selected pulse width isoutputted as the output signal. The pulse of this output signal may bearranged as follows. Namely, as is done in the hysteresis comparator 23,the pulse of the output signal may have a pulse width which is areproduction of the pulse width of the signal optical pulse beinginputted, and it is possible to generate such a pulse every time thesignal optical pulse is inputted. Alternatively, it is also possible touse a circuit provided in advance, which generates a pulse having afixed pulse width as is done in the switching circuit 12. Further, aperson in charge of designing may decide how to select and determine thepulse width of the output signal. For example, as described in thepresent embodiment, the receiving circuit may be so arranged, in themanufacturing process therefor, that one of signals respectively havingdifferent pulse widths is selectively outputted according to whether ornot the pulse width of the signal optical pulse is longer than thepredetermined value (T1). More specifically, the receiving circuit maybe so arranged as to: (I) output the output signal whose pulse width isthe same as that of the signal optical pulse, if the pulse width of thesignal optical pulse is equal to or less than the predetermined value(T1); or (II) output an output signal (e.g., the output signal having along pulse width for the low-speed communication) whose pulse width isdifferent from the pulse width of the signal optical pulse, if the pulsewidth of the signal optical pulse is longer than the predetermined value(T1). This makes it possible to output an appropriate output signal inaccordance with the signal optical pulse in the receiving circuit. Thus,without a need of a switching-over terminal, it is possible toautomatically specify the communication speed, and output the mostappropriate received output pulse in accordance with the communicationspeed.

Further, by increasing the number of stages for judging the pulse widthof the received input, the communication speed can be distinguished intothree or more ranges. This allows generation of the received outputpulse to be optimized for each of the ranges of the communication speed.

FIG. 2 is a block diagram illustrating another exemplary configurationof the equivalent circuit. A difference from the configuration shown inFIG. 1 is that a one-shot pulse generating circuit 41 is added to theoutput end of the comparator 23, so that the width of the output pulseduring the high-speed communication is kept constant. Conventionally,distortion of a waveform has been significant in a high-speedcommunication. This distortion of the waveform causes distortion in thepulse width and generation of wrong pulses. In order to avoid theseproblems, the pulse width of a signal being outputted is fixed at apredetermined pulse width by using a one-shot pulse generating circuitor the like. However, a wide pulse width which is suitable in alow-speed communication cannot be outputted when a pulse width of anoutputted one-shot pulse is fixed at a narrow pulse width for use in thehigh-speed communication. It is however possible to realize fixed pulsewidths optimized for various communication speeds by (I) using theautomatic switching-over system of the present invention, and (II)generating the one-shot pulse during the high-speed communication.

FIG. 3 is a block diagram illustrating yet another exemplaryconfiguration of the equivalent circuit. The configuration illustratedin FIG. 3 differs from that of FIG. 2 in that a delay circuit 42 isprovided in a stage subsequent to the one-shot pulse generating circuit41. This prevents a leading pulse of a signal row from being stretchedduring the low-speed communication. Note that the delay circuit 42 maybe directly provided in a stage directly subsequent to the hysteresiscomparator circuit 23, and the one-shot pulse generating circuit 41 maybe omitted.

More specifically, in the waveform chart of FIG. 6, a leading pulse ofthe VO waveform is wider than it supposed to be; i.e., wider than thepulse width of the second pulse and the successive pulses. This isattributed to such a setting that the pulse is outputted during theperiod (T1) taken to specify the communication speed, since start ofinputting of the set of pulses. This inevitably causes the leading pulseto stretch until the period (T1) is elapsed. In view of the foregoingproblem, the pulse of a node (i) in FIG. 6 is delayed as shown in FIG.7, so that the leading pulse is kept from being stretched. A delay timeTd is preferably longer than the first predetermined period (T1) for usein specifying the communication speed.

The value (length) of the first predetermined period (T1) shown in FIG.6 may be between values of respective pulse widths of two communicationspeeds to be distinguished from each other. More specifically, the valueof the T1 may be between (I) a value of the pulse width of the pulseoutputted from the hysteresis comparator circuit 23 serving as the firstpulse generating circuit, and (II) a value of the pulse width of thepulse outputted from the one-shot pulse generating circuit 34 serving asthe second pulse generating circuit. Note that, as mentioned before, thepulse width (T3) of the pulse outputted from the one-shot pulsegenerating circuit 34 is longer than the pulse width of the pulseoutputted from the hysteresis comparator circuit 23. The followingdescribes IrDA standard which is the common infrared data communicationstandard, with reference to an example. FIG. 8 shows pulse widths ofcommunication speeds used under IrDA standard. For example, it ispreferable to: (I) distinguish the communication speeds into (i) acommunication speed of 576 kbps or more, and (ii) a communication speedrange of 115.2 kbps or less; and then (II) output the received outputoptimized for the distinguished communication speed. In this case, theperiod (T1) for judging the communication speed may be set between (I)521 n sec. which is a maximum pulse width in a communication of 576kbps, and (II) 1.41 μsec. which is a minimum pulse width in acommunication of 115.2 kbps. The communication speed is more accuratelydistinguished by setting the T1 to a value nearby the mid point of thesepulse widths; i.e., about 0.9 to 1.0 μsec.

The second predetermined period (T2) may be as follows. Namely, T2 is aperiod (maintaining period) during which the status is maintained afterthe communication speed is specified. It is necessary that themaintaining period last until the communication ends. However, it is notpreferable that a resetting operation be required. This is because therequirement of the resetting operation necessitates a terminal andadditional control for the resetting operation. In order to overcomethis problem, the second predetermined period (T2) is set at a minimumamount of time required for maintaining the communication speed. On thisaccount, the maintaining period is extended by using a re-triggerableone-shot circuit for resetting the timer circuit every time a pulse isreceived.

For example, in IrDA standard which is the common infrared datacommunication standard, the lowest communication speed in the low speedcommunication is 9.6 kbps, and the maximum interval between a pulse andanother pulse is 1.04 m sec. Accordingly, the communication speed ismaintained without fail by setting the second predetermined period at1.04 m sec. or longer.

FIG. 4 shows still another configuration. In FIG. 4, a node (f) signal,which is a signal where the communication speed is specified, is usedfor: (I) switching over a frequency band and a gain of the amplifyingcircuit 22 for optimization so as to suit the communication speed; or(II) switching over a response speed of the first pulse generatingcircuit. In this case, the first pulse generating circuit is thevariable output circuit. This first pulse generating circuit includesthe hysteresis comparator circuit 23, and further includes, ifnecessary, the one-shot pulse generating circuit 41; a delay circuit 42;and the received output inverter circuit 39 provided at a leading end ofa node (k). In the example of FIG. 4, control is performed with respectto the received output inverter circuit 39.

The following provides more detailed description of the above, withreference to a configuration illustrated in FIG. 11. An opticalcommunication-use receiving circuit 102 illustrated in FIG. 11 has aconfiguration similar to the configuration shown in FIG. 9, and furtherincludes: a one-shot pulse generating circuit 81 connected to the outputof the hysteresis comparator circuit 23; and a received output invertercircuit 82 connected to an output OS_out of the one-shot pulsegenerating circuit 81. It is advantageous to switch over the responsespeed of the pulse generating circuit, and a processing speed of thereceived output circuit has been speeded up along with the accelerationof the communication speed. However, under such circumstances, aninfluence by an interference of the received input and the receivedoutput has become no longer ignorable. The interference causesdistortion in a waveform of an amplifier, and this distortion inducesvarious malfunctions. More specifically, the equivalent circuitillustrated in the block diagram of FIG. 11 has, between (I) thereceived output VO and (II) the received input section (PD section) orthe amplifying circuit, a capacitive coupling (coupling capacitanceC_cup) via resin or the like used for packaging. This causes thewaveform outputted from the amplifier to be distorted at a timing ofvoltage transition in the received output VO. The distorted waveformagain generates an unnecessary pulse at the comparator output. Usingthis unnecessary pulse as a trigger, a one-shot pulse is generated, andthis one-shot pulse generates an unnecessary pulse at the receivedoutput, thus causing a malfunction.

On the other hand, in a low-speed communication, the high-speed receivedoutput circuit is not required to respond at a high-speed. Therefore, inorder to reduce the influence from the capacitive coupling, the responsespeed of the output circuit is reduced during the low-speedcommunication. By having the configuration of FIG. 4, the receivingcircuit is optimized for the specified communication speed. Thisrealizes appropriate performance of the optical communication-usereceiving circuit, by acquiring an optimum S/N ratio according to thespecified communication speed.

As described, the following effects are obtained from the presentinvention. Namely, in the optical communication-use receiving circuit,the communication speed is automatically specified. This allows, withoutadding an external terminal for transmitting a communication speedswitching-over signal, realization of a status and a received pulse forthe specified communication speed. Further, communicating performancecan be improved by optimizing the receiving circuit for the specifiedcommunication speed.

An electronic device including the foregoing optical communication-usereceiving circuit for receiving an optical signal is not limited.Examples of such an electronic device are personal computer, mobilephone, PDA (Personal Digital Assistant).

A receiving circuit of the present invention may be for use in aninfrared data communication so adapted that (I) the receiving circuithas a circuit in which (a) a signal optical pulse incident to alight-receiving element is amplified by a light-receiving amplifier; and(b) a received output pulse is outputted as a digital signal generatedby comparing the output from the light-receiving amplifier with athreshold value and that (II) a pulse width of the received output pulseis automatically switched over in accordance with a pulse width of theinputted signal.

With the foregoing configuration, a switching over terminal which hasbeen conventionally required is no longer needed. Thus, it is possibleto easily reduce a size of a device having the receiving circuit.

A receiving circuit of the present invention for use in an infrared datacommunication may be so adapted that (I) the receiving circuit has acircuit in which (a) a signal optical pulse incident to alight-receiving element is amplified by a light-receiving amplifier and(b) a received output pulse is outputted as a digital signal generatedby comparing the output from the light-receiving amplifier with athreshold value; and that (II) the pulse width of the received signal isspecified; and (III) if the pulse width of the received signal is longerthan a predetermined pulse width, a circuit which outputs a pulse havinga pulse width which corresponds to a low-speed communication isactivated so as to output a pulse having a constant pulse width suitablefor the communication speed.

With the foregoing configuration, the switching over terminal which hasbeen conventionally required is no longer needed. Thus, it is possibleto easily reduce a size of a device having the receiving circuit.

A receiving circuit may further include: (I) a pulse generating circuitin which (a) a signal optical pulse incident to a light-receivingelement is amplified by a light-receiving amplifier and (b) a receivedoutput pulse is outputted as a digital signal generated by comparing theoutput from the light-receiving amplifier with a threshold value; (II) atrigger generating circuit for generating a trigger signal when a periodfor generating the pulse in the first pulse generating circuit is longerthan a first predetermined period; (III) a timer circuit for generatinga pulse of a second predetermined period in reception to the triggersignal generated by the trigger generating circuit; (IV) a one-shotpulse generating circuit for generating a pulse of a third predeterminedperiod; and (V) a logic such that (i) if the timer circuit outputs nopulse, the received output pulse is outputted as an ultimate output, and(ii) if the timer circuit outputs a pulse, a pulse of the one-shot pulsegenerating circuit is outputted as the ultimate output.

In the foregoing configuration, the communication speed is measured byspecifying the pulse width of the received pulse, in reference to thefirst predetermined period. If the pulse width is wider than the firstpredetermined period, it is acknowledged that the communication speed islow, and a pulse width for the low-speed communication is outputted. Onthe contrary, if the pulse width of the received pulse is shorter thanthe first predetermined period, it is acknowledged that thecommunication speed is high, and a pulse having a pulse width for thehigh-speed communication is outputted. With this configuration, it ispossible to easily and automatically switching over the pulse width ofthe outputted pulse.

Further, the receiving circuit of the present invention having theforegoing configuration may be so adapted that (I) the receiving circuithave a circuit in which (a) the signal optical pulse incident to thelight-receiving element is amplified by the light-receiving amplifier;and (b) the received output pulse is outputted as the digital signalgenerated by comparing the output from the light-receiving amplifierwith the threshold value; and that (II) the ultimate output is outputtedby adding a one-shot pulse generating circuit to the pulse generatingcircuit.

With the foregoing configuration, it is possible to prevent the pulsewidth of the received output to be distorted during the high-speedcommunication, and to prevent generation of a wrong pulse.

Further, the receiving circuit of the present invention having theforegoing configuration may be so adapted that (I) the receiving circuithave a circuit in which (a) the signal optical pulse incident to thelight-receiving element is amplified by the light-receiving amplifier;and (b) the received output pulse is outputted as the digital signalgenerated by comparing the output from the light-receiving amplifierwith the threshold value; and that (II) a one-pulse-delaying circuit isadded for outputting the ultimate output or (III) a one-shot pulsegenerating circuit is added and the one-pulse-delaying circuit isfurther added to the output of the one-shot pulse generating circuit.

This configuration prevents a leading pulse of a signal row from beingstretched at the time of acknowledging that the communication speed islow.

Further, the foregoing receiving circuit of the present invention may beso adapted that a value of the first predetermined period (T1) isbetween values of respective pulse widths of two communication speeds tobe distinguished from each other.

With the foregoing configuration, it is possible to most appropriatelyspecify the communication speed, in a case where a common infrared datacommunication standard IrDA is adopted. Specifically, it is possible to(I) distinguish the communication speed between (i) a communicationspeed of 576 kbps or more, and (ii) a communication speed of 115.2 kbpsor less, and (II) output a received output pulse optimized for thecommunication speed.

Further, the foregoing receiving circuit of the present invention may beso adapted that the first predetermined period is between 521 n sec. and1.41 μsec.

With the foregoing configuration, it is possible to most appropriatelyspecify the communication speed, in the case where the common infrareddata communication standard IrDA is adopted. Specifically, it ispossible to (I) distinguish the communication speed between (i) acommunication speed of 576 kbps or more, and (ii) a communication speedof 115.2 kbps or less, and (II) output a received output pulse optimizedfor the communication speed.

Further, the foregoing receiving circuit of the present invention may beso adapted that the second predetermined period is equal to or longerthan a maximum interval between a pulse and another pulse.

With the foregoing configuration, it is possible to optimize a periodfor specifying the communication speed and maintaining a status for thespecified communication speed, in the case where the common infrareddata communication standard IrDA is adopted. More specifically, when asignal row is being inputted at a speed of 115.2 kbps or lower, it ispossible to maintain the status without fail by setting the timer withwhich the second predetermined period is set so as to be equal to orlonger than the maximum interval between a pulse and another pulse.

Further, the foregoing receiving circuit of the present invention may beso adapted that the second predetermined period is 1.04 m sec. orlonger.

With the foregoing configuration, it is possible to optimize the periodfor specifying the communication speed and maintaining a status for thespecified communication speed, in the case where the common infrareddata communication standard IrDA is adopted. More specifically, when asignal row is being inputted at a speed of 115.2 kbps or lower, it ispossible to maintain the status without fail by setting the timer withwhich the second predetermined period is set so as to be equal to orlonger than the maximum interval between a pulse and another pulse.

Further, the foregoing receiving circuit of the present invention may beso adapted that a frequency band of the amplifying circuit or thecommunication speed of the output circuit is switched over during theperiod when the pulse of the second predetermined period exists, inaccordance with the communication speed of the amplifying circuit.

With the foregoing configuration, the performance of the receivingcircuit is optimized according to the specified communication speed.This realizes an optimum S/N ratio according to the specifiedcommunication speed.

Further an electronic device of the present invention may include anyone of the infrared data communication-use receiving circuit.

The present invention is applicable to a communication carried out byusing an infrared ray or the like.

The embodiments and concrete examples of implementation discussed in theforegoing detailed explanation serve solely to illustrate the technicaldetails of the present invention, which should not be narrowlyinterpreted within the limits of such embodiments and concrete examples,but rather may be applied in many variations within the spirit of thepresent invention, provided such variations do not exceed the scope ofthe patent claims set forth below.

1. A receiving circuit, for use in an optical communication, from whichan output signal is outputted in accordance with a signal optical pulseincident to a light-receiving element, the receiving circuit comprising:a variable output circuit for detecting a pulse width of the signaloptical pulse, selecting one pulse width from a plurality of pulsewidths in accordance with the pulse width thus detected, and outputtingan output signal having the one pulse width thus selected; the variableoutput circuit includes a first pulse generating circuit generating areceived pulse by comparing an electric signal converted from the signaloptical pulse with a threshold, the received pulse being a digitalsignal; wherein either the received pulse generated by the first pulsegenerating circuit or a pulse having a different pulse width from thatof the received pulse is selectively outputted as an output signal, inaccordance with the pulse width of the signal optical pulse; thevariable output circuit includes a second pulse generating circuit forgenerating a signal having a predetermined pulse width corresponding toa low-speed communication; and if it is judged that a pulse width of anoutput from the first pulse generating circuit exceeds a predeterminedvalue, a signal generated by the second pulse generating circuit isoutputted as the output signal, instead of outputting the receivedpulse; and the variable output circuit includes (I) a trigger generatingcircuit for generating a trigger signal when a pulse generating time ofthe first pulse generating circuit exceeds a first predetermined period,and (II) a timer circuit for generating a pulse having a secondpredetermined period, in response to the trigger signal from the triggergenerating circuit; if the timer circuit outputs no pulse, a pulseoutputted from the first pulse generating circuit is outputted as theoutput signal; and if the timer circuit outputs a pulse, a pulseoutputted from the second pulse generating circuit is outputted as theoutput signal.
 2. The receiving circuit as set forth in claim 1,wherein: a length of the first predetermined period is set between apulse width of the output pulse from the second pulse generating circuitand a pulse width of the output pulse from the first pulse generatingcircuit.
 3. The receiving circuit as set forth in claim 2, wherein thefirst predetermined period is between 521 n sec. and 1.41 μ sec.
 4. Thereceiving circuit as set forth in claim 1, wherein the secondpredetermined period is equal to or longer than a maximum intervalbetween a pulse and another pulse.
 5. The receiving circuit as set forthin claim 4, wherein the second predetermined period is 1.04 m sec. orlonger.
 6. The receiving circuit as set forth in claim 1, furthercomprising: an amplifying circuit for amplifying an electronic signalconverted from the signal optical pulse, the variable output circuitswitching over, in accordance with a communication speed, a frequencyband of the amplifying circuit during the period when the pulse of thesecond predetermined period exists.
 7. The receiving circuit as setforth in claim 1, wherein: during the period when the pulse of thesecond predetermined period exists, the variable output circuit switchesover a response speed of the variable output circuit, in accordance witha communication speed.
 8. A receiving circuit, for use in an opticalcommunication, from which an output signal is outputted in accordancewith a signal optical pulse incident to a light-receiving element, thereceiving circuit comprising: a variable output circuit for detecting apulse width of the signal optical pulse, selecting one pulse width froma plurality of pulse widths in accordance with the pulse width thusdetected, and outputting an output signal having the one pulse widththus selected; the variable output circuit includes a first pulsegenerating circuit generating a received pulse by comparing an electricsignal converted from the signal optical pulse with a threshold, thereceived pulse being a digital signal; wherein either the received pulsegenerated by the first pulse generating circuit or a pulse having adifferent pulse width from that of the received pulse is selectivelyoutputted as an output signal, in accordance with the pulse width of thesignal optical pulse; the variable output circuit includes a secondpulse generating circuit for generating a signal having a predeterminedpulse width corresponding to a low-speed communication; and if it isjudged that a pulse width of an output from the first pulse generatingcircuit exceeds a predetermined value, a signal generated by the secondpulse generating circuit is outputted as the output signal, instead ofoutputting the received pulse; and wherein the first pulse generatingcircuit includes a one-shot pulse generating circuit that receives thereceived pulse and maintains the pulse width of the output signal at aconstant value.
 9. The receiving circuit as set forth in claim 8,further comprising a delay circuit connected to an output of theone-shot pulse generating circuit.
 10. A receiving circuit, for use inan optical communication, from which an output signal is outputted inaccordance with a signal optical pulse incident to a light-receivingelement, the receiving circuit comprising: a variable output circuit fordetecting a pulse width of the signal optical pulse, selecting one pulsewidth from a plurality of pulse widths in accordance with the pulsewidth thus detected, and outputting an output signal having the onepulse width thus selected; the variable output circuit includes a firstpulse generating circuit generating a received pulse by comparing anelectric signal converted from the signal optical pulse with athreshold, the received pulse being a digital signal; wherein either thereceived pulse generated by the first pulse generating circuit or apulse having a different pulse width from that of the received pulse isselectively outputted as an output signal, in accordance with the pulsewidth of the signal optical pulse; the variable output circuit includesa second pulse generating circuit for generating a signal having apredetermined pulse width corresponding to a low-speed communication;and if it is judged that a pulse width of an output from the first pulsegenerating circuit exceeds a predetermined value, a signal generated bythe second pulse generating circuit is outputted as the output signal,instead of outputting the received pulse; and wherein the first pulsegenerating circuit includes a delay circuit to which the received pulseis inputted.
 11. A receiving circuit, for use in an opticalcommunication, from which an output signal is outputted in accordancewith a signal optical pulse incident to a light-receiving element, thereceiving circuit comprising: a variable output circuit for detecting apulse width of the signal optical pulse, determining a pulse width ofthe output signal in accordance with the pulse width of the signaloptical pulse, and outputting the output signal; wherein the variableoutput circuit includes a first pulse generating circuit generating areceived pulse by comparing an electric signal converted from the signaloptical pulse with a threshold, the received pulse being a digitalsignal; and wherein either the received pulse generated by the firstpulse generating circuit or a pulse having a different pulse width fromthat of the received pulse is selectively outputted as an output signal,in accordance with the pulse width of the signal optical pulse; whereinthe variable output circuit further includes a second pulse generatingcircuit for generating a signal having a predetermined pulse widthcorresponding to a low-speed communication; and if it is judged that apulse width of an output from the first pulse generating circuit exceedsa predetermined value, a signal generated by the second pulse generatingcircuit is outputted as the output signal, instead of outputting thereceived pulse; and wherein the variable output circuit still furtherincludes a trigger generating circuit for generating a trigger signalwhen a pulse generating time of the first pulse generating circuitexceeds a first predetermined period, and a timer circuit for generatinga pulse having a second predetermined period, in response to the triggersignal from the trigger generating circuit; if the timer circuit outputsno pulse, a pulse outputted from the first pulse generating circuit isoutputted as the output signal; and if the timer circuit outputs apulse, a pulse outputted from the second pulse generating circuit isoutputted as the output signal.